The present invention relates to compressor blades and methods of replacing compressor blades with blades having a different blade angle and particularly relates to compressor blades having a platform with one or more side flanges forming an extension for supporting a leading edge of the blade. The present invention also relates to such blades in combination with a modified compressor wheel groove and methods of retrofitting blades having a different blade angle than the blade angle of the blades being replaced on the wheel.
With the ever present need for higher performance and efficiency for compressors, new and improved blade designs have evolved with increased blade angles. For example, the higher performing and more efficient airfoils may have a greater twist than prior compressor blade airfoils and thus have a greater circumferential extent between leading and trailing edges in a direction along the periphery of the compressor wheel. It will be appreciated that the compressor wheel has a rim with a plurality of circumferentially spaced grooves for receiving bases of the compressor blades. For example, the groove may extend axially or slightly off axis and may comprise a dovetail configuration having a pair of circumferentially spaced radially outwardly converging side walls for receiving a correspondingly configured base attachment of the compressor blade. The blades are typically characterized as axial entry or slightly off axis entry blades. The blade base attachment has a radially outwardly facing platform surface which lies flush with the rim of the rotor wheel when the blade is installed. These configurations of blades and wheel grooves limit replacement of the blades to substantially identical blades. Otherwise, the entire compressor rotor wheel would require replacement to accommodate the newer higher performing and more efficient airfoils.
In large gas turbines used for generating electricity, power companies regularly water wash the turbines as soon as any performance degradation is noticed. The water wash is sprayed into the turbine near the hub at the compressor end and the fluid is flung out into the flow path cleaning the blades. As a result of this water wash, water droplets impact the first stage compressor blades causing significant erosion along the leading edges of the airfoils and especially at the hub of the airfoils where the airfoils meet the platform. Performance degradation and potential for failure of the airfoils causing extensive rotor damage oftentimes result. Consequently, there is a need to replace compressor blades when the airfoils are damaged, e.g., eroded due to water washing and foreign object damage, and more generally to provide blades with increased blade angles relative to the blade angles of the blades extant in the compressor.